Position Sizing Formula: From Stop Distance to Lot Size
Macro Glossary, Orders and Risk
By Ken Chigbo, macro trader and founder of KenMacro, 18+ years in markets.
Updated 2026-05-20
The desk’s answer
The position sizing formula converts a target risk percentage and a stop loss distance into the position size that makes the math work. The standard form for forex is: lot size = (account balance times risk percent) / (stop distance in pips times pip value per lot). On a 10,000-dollar account risking 1 percent (100 dollars) on a 40-pip EUR/USD stop with a 10-dollar pip value per standard lot: lot size = 100 / (40 times 10) = 0.25 standard lots. The formula does not care about leverage. It cares about balance, risk percent, stop distance and pip value, and it produces a single correct lot size for each trade.
Defined term, Position sizing formula
The position sizing formula is the deterministic calculation that converts a target risk percentage and a stop loss distance into the appropriate position size for a trade. The standard form is: position size = (account balance multiplied by risk percent) divided by (stop distance multiplied by pip value or point value per unit). It is the single most important calculation in survivable risk management.
The forex formula
Position size in lots = (account balance times risk percent) divided by (stop distance in pips times pip value per lot in the account currency). For a USD account on EUR/USD, pip value per standard lot is 10 dollars. For a USD account on yen pairs, pip value per standard lot is approximately 1,000 divided by USD/JPY (so roughly 6.50 dollars per pip at a USD/JPY of 155). For a USD account on a non-USD-quote pair (e.g. EUR/GBP), the pip value requires an extra conversion through the cross rate. Most modern broker platforms include a position-size calculator that handles this automatically; the formula is essential to understand because it makes the trader’s sizing deterministic rather than discretionary.
The equity-account formula
For indices, stocks and CFDs the same logic applies but the units change. Position size in contracts (or shares) = (account balance times risk percent) divided by (stop distance in points times point value per contract). On the S and P 500 mini futures (ES) with a point value of 50 dollars per point, a 10-point stop on a 1-percent-risk trade from a 25,000 dollar account requires position size = 250 / (10 times 50) = 0.5 contracts, which on ES rounds to 0 (you cannot trade fractional contracts) and requires either a smaller account, a wider stop, or trading the micro S and P 500 (MES, 5 dollars per point) instead.
Why this is the most important calculation
Three reasons. First, it forces deterministic sizing: the position size is whatever the formula returns, not whatever the trader wants to trade. This eliminates the dominant retail error of sizing by leverage rather than by stop distance. Second, it makes risk per trade consistent across instruments: a 1-percent risk on EUR/USD and a 1-percent risk on gold produce different lot sizes but the same dollar exposure to the stop, so the strategy compounds in R consistently. Third, it disciplines the trader to define the stop before the position size, which is the correct sequence and the one that almost all retail strategies get backwards.
Frequently asked
What is the position sizing formula?
Lot size = (account balance times risk percent) divided by (stop distance in pips times pip value per lot). For a 10,000-dollar account risking 1 percent on a 40-pip EUR/USD stop, lot size = 100 / (40 times 10) = 0.25 standard lots. The formula determines position size deterministically from risk percent and stop distance.
Does leverage affect position sizing?
No. Leverage only affects the margin required to hold a position, not the size of the position or the risk taken. Position sizing is determined by stop distance and risk percent. Sizing by leverage is the dominant retail error and leads to over-sized positions that get stopped out on normal moves.
What if the formula returns a lot size smaller than the broker minimum?
Either widen the stop (if structurally justified), reduce the risk percent below 1 percent for this specific trade, or trade a smaller-contract product (micro lots, micro futures). Never increase the position size beyond what the formula returns just to meet a broker minimum; that is sizing by what the broker permits, not by what the math requires.
What this means at the desk
Run the formula on every trade. The stop sets the size; nothing else does.
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